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Catalytic Hydroprocessing of Liquid Biomass for Biofuels Production · PDF file 2013. 3. 18. · Catalytic pyrolysis Catalytic reforming Heavy Gasoil Hydrotreating Lubricants process

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  • Chapter 9

    Catalytic Hydroprocessing of Liquid Biomass for Biofuels Production

    Stella Bezergianni

    Additional information is available at the end of the chapter

    http://dx.doi.org/10.5772/52649

    1. Introduction

    The depletion of world petroleum reserves and the increased concern on climate change has stimulated the recent interest in biofuels. The most common biofuels are based on energy crops and their products, i.e. vegetable oil for Fatty Acid Methyl Esters (FAME) biodiesel [1] and sugars/starch for bioethanol. However these first generation biofuels and associated production technologies face several considerations related to their economic and social im‐ plications regarding energy crops cultivation, by-products disposal, necessity for large in‐ vestments to ensure competitiveness and the “food versus fuel” debate.

    As a result, second generation biofuel technologies have been developed to overcome the limitations of first generation biofuels production [2]. The goal of second generation biofuel processes is to extend biofuel production capacity by incorporating residual biomass while increasing sustainability. This residual biomass consists of the non-food parts of food crops (such as stems, leaves and husks) as well as other non-food crops (such as switch grass, ja‐ tropha, miscanthus and cereals that bear little grain). Furthermore the residual biomass po‐ tential is further augmented by industrial and municipal organic waste such as skins and pulp from fruit pressing, waste cooking oil etc. One such technology is catalytic hydropro‐ cessing, which is an alternative conversion technology of liquid biomass to biofuels that is lately raising a lot of interest in both the academic and industrial world and is the proposed subject of this chapter.

    Catalytic hydroprocessingis a key process in petrochemical industry for over a century ena‐ bling heteroatom (sulfur, nitrogen, oxygen, metals) removal, saturation of olefins and aro‐ matics, as well as isomerization and cracking [3]. Due to the numerous applications of catalytic hydroprocessing, there are several catalytic hydroprocessing units in a typical re‐ finery including distillate hydrotreaters and hydrocrackers (see Figure 1). As a result several

    © 2013 Bezergianni; licensee InTech. This is an open access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

  • refinery streams are treated with hydrogen in order to improve final product quality includ‐ ing straight-run naphtha, diesel, gas-oils etc. The catalytic hydroprocessing technology is evolving through the new catalytic materials that are being developed. Even though hydro‐ processing catalysts development is well established [4], the growing demand of petroleum products and their specifications, which are continuously becoming stricter, have created new horizons in the catalyst development in order to convert heavier and lower quality feedstocks [5]. Furthermore the expansion of the technology to bio-based feedstocks has also broadened the R&D spam of catalytic hydrotreatment.

    Thermal process

    Heavy fractions

    upgrading

    Catalytic pyrolysis

    Catalytic reforming

    Heavy Gasoil

    Hydrotreating

    Lubricants process

    Naphtha

    Light Vacuum Gasoil

    Heavy Vacuum Gasoil

    Coke

    Asphalt

    Lubricants

    Thermal processing

    Hydrocracking mid-distillate

    Hydrocracking gasoline

    Light hydrocarbons C1-C4

    Isomerization product

    Reformate

    Gasoline polymerization

    Alkylate

    Alkylation gasoiline

    Straight-run kerozene

    Straight-run diesel

    Catalytic pyrolysis gasoline

    Catalytic pyrolysis

    F in

    al p

    ro ce

    ss in

    g a

    n d

    b le

    n d

    in g

    Fuel gas

    Liquid gas

    Aviation

    Diesel

    Unleaded

    Heating

    Gasoline

    oil

    Fuels

    Hydrotreating

    Hydrotreating

    Fuel gas and gasoline

    diesel

    Hydrocracking

    Atm. Distillation

    Vacuum Distillation

    Isomerization

    Polymerization

    Alkylation

    Thermal process

    Heavy fractions

    upgrading

    Catalytic pyrolysis

    Catalytic reforming

    Heavy Gasoil

    Hydrotreating

    Lubricants process

    Naphtha

    Light Vacuum Gasoil

    Heavy Vacuum Gasoil

    Coke

    Asphalt

    Lubricants

    Thermal processing

    Hydrocracking mid-distillate

    Hydrocracking gasoline

    Light hydrocarbons C1-C4

    Isomerization product

    Reformate

    Gasoline polymerization

    Alkylate

    Alkylation gasoiline

    Straight-run kerozene

    Straight-run diesel

    Catalytic pyrolysis gasoline

    Catalytic pyrolysis

    F in

    al p

    ro ce

    ss in

    g a

    n d

    b le

    n d

    in g

    Fuel gas

    Liquid gas

    Aviation

    Diesel

    Unleaded

    Heating

    Gasoline

    oil

    Fuels

    Hydrotreating

    Hydrotreating

    Fuel gas and gasoline

    diesel

    Hydrocracking

    Atm. Distillation

    Vacuum Distillation

    IsomerizationIsomerization

    PolymerizationPolymerization

    AlkylationAlkylation

    Figure 1. Catalytic hydroprocessing units within a refinery, including distillate hydrotreating and hydrocracking

    Catalytic hydroprocessing of liquid biomass is a technology that offers great flexibility to the continuously increasing demands of the biofuels market, as it can convert a wide variety of liquid biomass including raw vegetable oils, waste cooking oils, animal fats as well as al‐ gal oils into biofuels with high conversion yields. In general this catalytic process technolo‐ gy allows the conversion of triglycerides and lipids into paraffins and iso-paraffins within the naphtha, kerosene and diesel ranges. The products of this technology have improved characteristics as compared to both their fossil counterparts and the conventional biofuels including high heating value and cetane number, increased oxidation stability, negligible acidity and increased saturation level. Besides the application of this catalytic technology for the production of high quality paraffinic fuels, catalytic hydroprocessing is also an effective

    Liquid, Gaseous and Solid Biofuels - Conversion Techniques300

  • technology for upgrading intermediate products of solid biomass conversion technologies such as pyrolysis oils and Fischer-Tropsch wax (Figure 2). The growing interest and invest‐ ments of the petrochemical, automotive and aviation industries to the biomass catalytic hy‐ droprocessing technology shows that this technology will play an important role in the biofuels field in the immediate future.

    Gasification Wax

    Solid Biomass Pyrolysis oilPyrolysis Catalytic

    Hydroprocessing

    Liquid Biomass

    Gasoline Diesel

    Fischer-Tropsch SynthesisGasification

    Wax

    Solid Biomass Pyrolysis oilPyrolysis Catalytic

    Hydroprocessing

    Liquid Biomass

    Gasoline Diesel

    Fischer-Tropsch Synthesis

    Figure 2. Catalytic hydroprocessing for biomass conversion and upgrading towards fuels production

    In the sections that follow, the basic technical characteristics of catalytic hydrotreatment are presented including a description of the process, reactions, operating parameters and feed‐ stock characteristics. Furthermore key applications of catalytic hydroprocessing of liquid bi‐ omass are outlined based on different feedstocks including raw vegetable oils, waste cooking oils, pyrolysis oils, Fischer-Tropsch wax and algal oil, and some successful demon‐ stration activities are also presented.

    2. Technical characteristics of catalytichydrotreatment

    The catalytic hydrotreatment of liquid biomass converts the contained triglycerides/lipids into hydrocarbons at high temperatures and pressures over catalytic material under excess hydrogen atmosphere. The catalytic hydrotreatment of liquid biomass process is quite simi‐ lar to the typical process applied to petroleum streams, as shown in Figure 3. A typical cata‐ lytic hydrotreatment unit consists of four basic sections: a) feed preparation, b) reaction, c) product separation and d) fractionation.

    In the feed preparation section the liquid biomass feedstock is mixed with the high pressure hydrogen (mainly from gas recycle with some additional fresh make-up hydrogen) and is preheated before it enters the reactor section. The reactor section consists normally of two hydrotreating reactors, a first guard mild hydrotreating reactor and a second one where the main hydrotreating reactions take place. Each reactor contains two or more catalytic beds in order to maintain constant temperature profile throughout the reactor length. Within the re‐ actor section all associated reactions take place, which will be presented in more detail at a later paragraph.

    Catalytic Hydroprocessing of Liquid Biomass for Biofuels Production http://dx.doi.org/10.5772/52649

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  • The reactor product then enters the separator section where, after it is cooled down, it enters the high pressure separator (HPS) flash drum in which the largest portion of the gas and liq‐ uid product molecules are separated. The gas product of the HPS includes

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